/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 36 Casey is driving a \(1600 \mathr... [FREE SOLUTION] | 91Ó°ÊÓ

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Casey is driving a \(1600 \mathrm{kg}\) car toward the east. She goes through an intersection at a speed of \(16 \mathrm{m} / \mathrm{s}\) (approximately \(35 \mathrm{mph}),\) the speed limit on both roads of the intersection. Kerry is driving a car of mass \(1200 \mathrm{kg}\) into the intersection, going north, and doesn't see or doesn't heed a red light, and slams into Casey's car. The cars lock together and skid to a stop. Later, the two review the scene with the police. Skid marks from the instant after the collision reveal that the two cars were moving exactly northeast. Kerry claims to have been driving at the speed limit, but Casey says that Kerry seemed to be going over the speed limit before the collision. Who is correct? Use the concept of conservation of momentum to make your case.

Short Answer

Expert verified
Based on the principle of conservation of momentum, it is determined that Kerry's pre-collisional speed was 21.33 m/s- higher than the speed limit, indicating that Casey's claim is correct.

Step by step solution

01

Understand the Principle of Momentum Conservation

The principle of momentum conservation states that the total momentum before the collision equals total momentum after the collision, assuming no external forces are acting upon the system. Momentum, denoted as \( p \), is the product of an object's mass (\( m \)) and its velocity (\( v \)). It is a vector and thus has both magnitude and direction. Therefore, we need to consider these two directions, i.e., east and north, independently.
02

Setting Up the Equations for Momentum Conservation

Before the collision, the momentum of Casey's car going east is \( p_{C1} = m_C * v_C = 1600 \, kg * 16 \, m/s = 25600 \, kg*m/s \) and Kerry's car going north with unknown velocity \( v_k \), hence the momentum is \( p_{K1} = m_k * v_k = 1200 \, kg * v_k \). After the collision, the cars are moving northeast, meaning the momentum has the same magnitude in both directions, i.e., north and east. Thus, we gather from these two relationships: \( p_{C2_{east}} = p_{C1} = 25600 \, kg*m/s \), and \( p_{C2_{north}} = p_{K2} = p_{K1} = 1200 \, kg * v_k \).
03

Solving for the Unknown Speed

Since the total momentum in the east and north directions must be equal after the collision, we have \( p_{C2_{east}} = p_{C2_{north}} \). Hence, \( 25600 \, kg*m/s = 1200 \, kg * v_k \). Solving for \( v_k \) gives us \( v_k = \frac {25600 \, kg*m/s} {1200 \, kg} \), yielding \( v_k = 21.33 \, m/s \).
04

Conclusion

Casey's assertion is correct. Kerry was indeed driving over the speed limit before the collision. This is evident from the calculated speed of Kerry's car, which exceeds the speed limit of 16 m/s (approximately 35 mph).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Collision Analysis
Collision analysis is a vital method in understanding interactions between moving objects, such as vehicles. Collisions occur when two or more objects come into contact while in motion. Depending on whether the motion continues after impact without separation, they can be classified as elastic or inelastic. In this scenario, both vehicles lock together immediately after the collision, indicating a perfectly inelastic collision.

During such inelastic collisions, the two objects move together as one unit post-impact. The direction and speed of the resultant movement depend on the masses and velocities of the involved objects before the collision. Analyzing these interactions helps determine the conditions before and after a collision and deduce any discrepancies in speed or trajectory claims.

This analysis extends the understanding of real-life motion elements like velocity, direction, and mass. It is a crucial investigative tool for scenarios like traffic accidents, providing insights based on scientific calculations instead of solely relying on personal observations.
Momentum Conservation Equations
The principle of momentum conservation is fundamental in physics, especially in analyzing collision scenarios. This principle asserts that the total momentum of a closed system remains constant over time, given no external forces impact the system. In the context of a collision, it indicates that the combined momentum of all parties before the crash must equal the total momentum after.

The momentum equation for each object involves multiplying its mass by its velocity. Therefore, for a collision involving cars, the momentum of each vehicle can be expressed as follows:
  • Momentum of Casey's car is given by \(1600 \, \text{kg} \times 16 \, \text{m/s} = 25600 \, \text{kg}\cdot\text{m/s}\)
  • Momentum of Kerry's car is \(1200 \, \text{kg} \times v_k\), where \(v_k\) is the unknown speed.
After the collision, if the cars lock together moving in a common direction (northeast), their combined momentum paths must equate to the initial separate paths. Understanding and applying these equations can immediately indicate discrepancies in pre-collision speeds based on observed post-collision dynamics.
Vehicle Mass and Velocity
A vehicle's mass and velocity significantly influence its momentum and subsequently affect collision outcomes. In our scenario, Casey's vehicle has a mass of 1600 kg and moves at a velocity of 16 m/s east. These factors combine to give it a substantial momentum directed eastward.

Kerry's vehicle, with a mass of 1200 kg, may have a varied northward velocity, which we solved to be approximately 21.33 m/s through momentum conservation calculations in the east-north path analysis. This value exceeded the legal velocity limit, confirming the violation.

The mass and velocity details are used in conservation equations to compute real-time motion effects and post-accident behavior. Understanding how mass and velocity interact under collision scenarios is essential in practical applications, such as vehicle safety designs, traffic regulation enforcements, and technical safety evaluations in crash investigations.

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Most popular questions from this chapter

I trap-jaw ant snaps its mandibles shut at very high speed, a good trait for catching small prey. But an ant can also slam its mandibles into the ground; the resulting force can launch the ant into the air for a quick escape. A 12 mg ant hits the ground with an average force of \(47 \mathrm{mN}\) for a time of \(0.13 \mathrm{ms} ;\) these are all typical values. At what speed does it leave the ground?

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Ill A diver leaves the platform with her body straight. Her body is in a relatively slow rotation, with an angular speed of \(4.0 \mathrm{rad} / \mathrm{s}\). She then tucks into a pike position, with her body essentially folded in half. We can use a simple model to understand what happens next. First, model her \(50 \mathrm{kg}, 1.8 \mathrm{m}\) body as uniform. Next, assume that when she goes into a pike position, she really does fold her body exactly in half. In terms of this model, a. What is her initial moment of inertia? b. What is her moment of inertia in the pike position? c. What is her angular speed in the pike position? d. How many rotations does she complete in the \(1.3 \mathrm{s}\) that she holds the pike position?

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